Dynamic recrystallization of austenite in Ni-30 Pct Fe model alloy : microstructure and texture evolution

The microstructure and crystallographic texture development in an austenitic Ni-30 pct Fe model alloy was investigated within the dynamic recrystallization (DRX) regime using hot torsion testing. The prominent DRX nucleation mechanism was strain-induced grain boundary migration accompanied by the formation of large-angle sub-boundaries and annealing twins. The increase in DRX volume fraction occurred through the formation of multiple twinning chains. With increasing strain, the pre-existing Σ3 twin boundaries became gradually converted to general boundaries capable of acting as potent DRX nucleation sites. The texture characteristics of deformed grains resulted from the preferred consumption of high Taylor factor components by new recrystallized grains. Similarly, the texture of DRX grains was dominated by low Taylor factor components as a result of their lower consumption rate during the DRX process. The substructure of deformed grains was characterized by “organized,” banded subgrain arrangements, while that of the DRX grains displayed “random,” more equiaxed subgrain/cell configurations.

Texture and substructure development during dynamic recrystallization in Ni-30Fe austenite

An austenitic Ni-30%Fe model alloy was employed to investigate the texture and substructure development within the deformed matrix and dynamically recrystallized (DRX) grains during hot torsion deformation. Both the deformed matrix and DRX grains predominantly displayed the crystallographic texture components expected for simple shear deformation. The characteristics of the deformed matrix texture evolution during deformation largely resulted from the preferred consumption of high Taylor factor components by new recrystallized grains. Likewise, the comparatively weaker crystallographic texture of DRX grains became increasingly dominated by low Taylor factor components as a result of their easier nucleation and lower consumption rate during DRX. There was a significant difference in the substructure formation mechanism between the deformed matrix and DRX grains for a given texture component. The deformed matrix substructure was largely characterized by “organized”, banded subgrain arrangements with alternating misorientations, while the substructure of DRX grains was more “random” in character and displayed complex, more equiaxed subgrain/cell arrangements characterized by a local accumulation of misorientations. Substructure characteristics of individual orientation components were principally consistent with the corresponding Taylor factor values.

Texture and substructure characteristics of dynamic recrystallization in a Ni–30%Fe austenitic model alloy

The substructure and texture development during dynamic recrystallization (DRX) of an austenitic Ni–30%Fe model alloy was investigated using hot torsion testing. The current results revealed that the DRX texture was dominated by grains with a low Taylor factor component. This was related to the preferred nucleation and lower consumption rates of these grains during DRX. The substructure of DRX grains was ‘‘random” in character and displayed complex subgrain/cell arrangements that largely depended on grain orientation.

Texture and substructure development during post-dynamic softening in Ni-30%Fe austenite

The texture and substructure development during post-dynamic annealing of an austenitic Ni-30%Fe model alloy after complete dynamic recrystallization was investigated using electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). A novel mechanism of metadynamic softening is proposed based on the experimental investigation of the grain structure, crystallographic texture and dislocation substructure evolution. The initial softening stage involved rapid growth of the dynamically formed nuclei and migration of the mobile boundaries. The subboundaries within DRX grains progressively disintegrated through dislocation climb and dislocation annihilation, which ultimately led to the formation of dislocation-free grains, while the grain boundary migration gradually became slower. As a result, the DRX texture was largely preserved throughout the annealing process.

Influence of deformation conditions and texture on the high temperature flow stress of magnesium AZ31

The evolution of hot working flow stress with strain is examined in torsion, uniaxial compression and channel die compression. The flow stress was found to be strongly dependent on texture and deformation mode. At low strains this dependency accounted for a difference in flow stress of up to a factor of two. At higher strains the influence of texture and deformation mode was less marked. The stresses corresponding to an equivalent strain of 0.5 were modelled using a power law expression with an activation energy of 147 kJ/mol and a strain rate exponent of 0.15. The influence of texture and deformation mode on flow stress is rationalised in terms of the influence of prismatic slip, twinning and dynamic recrystallisation on deformation stress and structure.

The influence of solute carbon in cold-rolled steels on shear band formation and recrystallization texture

Two experiments were conducted to clarify the roles of grain size, solute carbon and strain in determining the recrystallization textures of cold-rolled and annealed steels. In the first experiment, samples of coarse-grained low-carbon (LC) and interstitial-free (IF) steels were cold-rolled to a 75% reduction in thickness. One sample from each steel was polished and cold-rolled an additional 5%, while the remaining samples were annealed for various times at 650°C. In the second experiment, three samples from a commercial LC steel sheet were rolled 70% at 300°C. Two of the samples were given a further rolling reduction of 5% of the original thickness, with one of the samples being given this additional reduction at 300°C and the other at room temperature. Goss recrystallization textures are strengthened by coarse initial grain sizes, the presence of solute carbon and rolling at a temperature where dynamic strain ageing occurs, but are weakened by additional rolling beyond a reduction of 70%, especially when this extra rolling is conducted at a temperature where dynamic strain ageing does not occur. Characterization of key features of the deformed and recrystallized steels using optical microscopy, scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD) supports a rationale for these effects based on the repeated activation and deactivation of shear bands and the influence of solute carbon and dynamic strain ageing on the operating life of the bands and the accumulation of strain within them.

The mechanism of metadynamic softening in austenite after complete dynamic recrystallization

A novel mechanism of post-dynamic softening during annealing of a fully dynamically recrystallized (DRX) austenitic Ni–30Fe alloy is proposed. The initial softening stage involves rapid growth of the dynamically formed nuclei and migration of the mobile boundaries. The sub-boundaries within DRX grains progressively disintegrate through dislocation climb and dislocation annihilation, which ultimately leads to the formation of dislocation-free grains, and the grain boundary migration gradually becomes slower. As a result, the DRX texture largely remains preserved throughout the annealing process.

On the characteristics of substructure development through dynamic recrystallization

Substructure development in an austenitic Ni-30%Fe model alloy was investigated within a dynamic recrystallization (DRX) regime. The substructure characteristics of the deformed matrix and DRX grains were markedly different regardless of the grain size and orientation. The former largely displayed 'organized', banded subgrain arrangements with alternating misorientations, resulting from a limited number of active slip systems. In contrast, the substructure of DRX grains was generally more 'random' and exhibited complex subgrain/cell arrangements characterized by local accumulation of misorientations, suggesting multiple slip. The proposed mechanism of the unique substructure development within DRX grains suggests that the DRX nuclei, forming along pre-existing grain boundaries and triple points, essentially represent grain boundary regions, which experience multiple slip to preserve the compatibility with neighbouring deformed grains. This results in the formation of a complex cell/subgrain structure, which progressively extends as the grain boundary regions expand outwards during DRX growth.

Substructure development through dynamic recrystallisation in an austenitic Ni–30%Fe alloy

This data looks at the effect of grain boundary movement on the characteristics of substructure development within the DRX regime. Different thermo-mechanical processing routes were employed to produce a range of DRX grain sizes at a given deformation temperature. The development of dislocation substructure was investigated using electron back-scattered diffraction (EBSD) in conjunction with transmission electron microscopy (TEM).

On the characteristics of substructure development through dynamic recrystallization

This body of data is the result of an investigation into the effect of grain boundary movement on the characteristics of substructure development in an austenitic Ni-30%Fe model alloy within the DRX regime. Different thermo-mechanical processing routes were employed to produce a range of DRX grain sizes at a given deformation temperature. The development of dislocation substructure was investigated using electron back-scattered diffraction (EBSD) in conjunction with transmission electron microscopy (TEM).

Texture evolution and softening processes in an austenitic Ni-30Fe alloy subjected to hot deformation and subsequent annealing

The current work has investigated the texture development in an austenitic Ni-30Fe model alloy during deformation within the dynamic recrystallization (DRX) regime and after post-deformation annealing. Both the deformed matrix and DRX texture displayed the expected FCC shear components, the latter being dominated by the low Taylor factor grains, which was presumably caused by their lower consumption rate during DRX. The deformed matrix grains were largely characterized by organized, microband structures, while the DRX grains showed more random, complex subgrains/cell arrangements. The latter substructure type proved to be significantly less stable during post-deformation annealing. The recrystallization of the deformed matrix occurred through nucleation and growth of new grains fully replacing the deformed structure, as expected for the classical static recrystallization (SRX). Unlike the DRX grains, the SRX texture was essentially random. By contrast, a novel softening mechanism was revealed during annealing of the fully DRX microstructure. The initial post-dynamic softening stage involved rapid growth of the dynamically formed nuclei and migration of the mobile boundaries in line with the well-established metadynamic recrystallization (MDRX) mechanism, which weakened the starting DRX texture. However, in parallel, the sub-boundaries within the deformed DRX grains progressively disintegrated through dislocation climb and dislocation annihilation, which ultimately led to the formation of dislocation-free grains. Consequently, the weakened DRX texture largely remained preserved throughout the annealing process.

Substructure and texture development in austenite through thermomechanical processing

The data collection was performed using EBSD and TEM techniques. The objective was to characterise the substructure and crystallographic texture development during dynamic and post-dynamic deformation. The work reveals the role of the initial dislocation structure and texture on the softening characteristics in austenite and how these evolve during softening. It is also shown that the differences in the deformation dislocation structures between the dynamically recrystallized and deformed regions play a major role in determining the extent of recovery. An enhanced static recovery can be seen during post dynamic softening.

Substructure and texture characteristics of the deformed matrix and dynamically recrystallized grains in a Ni-30%Fe austenitic alloy

The substructure and crystallographic texture characteristics of both the deformed matrix and dynamically recrystallized (DRX) grains were investigated in a Ni-30%Fe austenitic model alloy subjected to hot torsion. Deformation was performed at a temperature of 1000°C using strain rates of 1, 0.1 and 0.01 s-1, which produced a range of DRX grain sizes. Electron back-scattered diffraction and transmission electron microscopy were employed in the investigation. Both the deformed matrix and DRX grains revealed the texture components expected for simple shear deformation by crystallographic slip. The texture of DRX grains was dominated by low Taylor factor components as a result of their lower consumption rate during growth of these grains. There was a marked difference in the substructure characteristics between the deformed matrix and DRX grains regardless of the grain size and orientation. The deformed matrix substructure was largely characterized by organized, banded subgrain arrangements with alternating misorientations. By contrast, the substructure of DRX grains was generally more random in character and displayed complex, more equiaxed subgrain/cell arrangements characterized by local accumulation of misorientations. Based on the experimental observations, a mechanism of the distinct substructure development within DRX grains has been proposed.

New insights into the dynamic and metadynamic recrystallization of austenite

The present work provides a summary of the recent findings obtained from the experimental investigation of the grain structure, crystallographic texture and dislocation substructure evolution in an austenitic Ni-30%Fe model alloy during dynamic recrystallization (DRX) and post-dynamic annealing. It has been found that the DRX texture characteristics become increasingly dominated by the low Taylor factor grains during DRX development, which presumably results from the preferred nucleation and lower consumption rates of these grains. The substructure of DRX grains is “random” in character and displays complex, hierarchical subgrain/cell arrangements characterized by accumulation of misorientations across significant distances. The stored energy within DRX grains appears to be principally consistent with the corresponding Taylor factor values. The changes observed within the fully dynamically recrystallized microstructure during postdynamic annealing have provided a basis to suggest a novel mechanism of metadynamic softening for the current experimental conditions. It is proposed that the initial softening stage involves rapid growth of the dynamically formed nuclei and migration of the mobile boundaries. The subboundaries within DRX grains progressively disintegrate through dislocation climb and dislocation annihilation, which ultimately leads to the formation of dislocation-free grains, and the grain boundary migration gradually becomes slower. As a result, the DRX texture largely remains preserved throughout the annealing process.

Effect of twinning on microstructural evolution during dynamic recrystallisation of hot deformed as-cast austenitic stainless steel

An as-cast austenitic stainless steel was hot deformed at 1173 K, 1223 K, and 1373 K (900 °C, 950 °C, and 1100 °C) to a strain of 1 with a strain rate of 0.5 or 5 s⁻¹. The recrystallised fraction is observed to be dependent on dynamic recrystallisation (DRX). DRX grains nucleated at the initial stages of recrystallization have similar orientation to that of the deformed grains. With increasing deformation, Cube texture dominates, mainly due to multiple twinning and grain rotation during deformation.